Embodiments of the invention relate generally to a hyperpolarized media for use in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy and, more particularly, to a vessel for transporting such a hyperpolarized media from a production source to an imaging system.
MRI and NMR spectroscopy are techniques that exploit the magnetic properties of certain atomic nuclei. With particular regard to MRI, a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), causing the individual magnetic moments of the spins in the tissue to attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which frequency is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is generated by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques. It is desirable that the imaging process, from data acquisition to reconstruction, be performed as quickly as possible for improved patient comfort and throughput.
One drawback to MRI and NMR spectroscopy is that they lack sensitivity due to the normally very low polarization of the nuclear spins of the samples used and/or substances being imaged. A number of techniques exist to improve the polarization of nuclear spins in the solid phase. These techniques are known as hyperpolarization techniques and lead to an increase in sensitivity. In hyperpolarization techniques, a sample of an imaging agent, for example 13C Pyruvate or another similar polarized metabolic imaging agent, is introduced or injected into the subject being imaged. As used herein, the term “polarize” refers to the modification of the magnetic properties of a material for further use in MRI. Further, as used herein, the term “hyperpolarized” refers to polarization to a level over that found at room temperature and 1 T.
However, while hyperpolarized media is highly effective in improving the polarization of nuclear spins for MRI and NMR spectroscopy, it is recognized that the magnetic polarization of the hyperpolarized media has a short lifetime—with relaxation occurring in a matter of seconds to minutes, therefore requiring the media to be used in the MRI as soon as possible after hyperpolarization. This short lifetime of the magnetic polarization of the hyperpolarized media can be problematic since the polarized sample is often transported to the MRI unit from a hyperpolarizing apparatus that is located outside of the MRI imaging suite, requiring an operator to physically transport the hyperpolarized media from the hyperpolarizer to the MRI unit.
The short lifetime of the hyperpolarized media can be further negatively affected if the hyperpolarized media is not maintained in a suitable magnetic field. That is, movement of the media through a zero magnetic field or low background magnetic field below 1-2 Gauss (e.g., the background magnetic field generated by the MRI unit) can further shorten the lifetime of the hyperpolarized media. In order to address this problem, one solution has been to provide a specially designed vessel for transporting the hyperpolarized media between the hyperpolarizing apparatus and the MRI unit.
In one prior art vessel, a hollow transport vessel was designed with permanent magnetic material arranged inside designed to generate a suitable and stable background magnetic field for transporting the hyperpolarized media from the hyperpolarizer apparatus to the MRI unit, so as to maintain the hyperpolarized state of the media. However, such a permanent magnet transport vessel has several drawbacks, including: an inability to control the strength of the magnetic field generated by the vessel, significant inhomogeneity of the background magnetic field created inside the vessel, and the inability to turn the magnetic field off—which can cause the device to be interact with the MRI magnet with great force when brought in the vicinity of the MRI unit, such as by being attracted to or expelled from the magnet or being caused to twist/torque in the presence of the magnet.
Therefore, it is desirable to provide a transport solution that can safely and efficiently provide a suitable background magnetic field that is stable (homogenous magnetic field around hyperpolarized media) and preserves the lifetime of the hyperpolarized media. It would further be desirable for such a transport solution to be made of non-magnetic materials and equipped with a mechanism that enables selective generation of such a background magnetic field, so as to provide for disengaging of the magnetic field when necessary.